var i = 5;

// s is compiled as a string
var s = "Hello";

// a is compiled as int[]
var a = new[] { 0, 1, 2 };

// expr is compiled as IEnumerable<Customer>
// or perhaps IQueryable<Customer>
var expr =
    from c in customers
    where c.City == "London"
    select c;

// anon is compiled as an anonymous type
var anon = new { Name = "Terry", Age = 34 };

// list is compiled as List<int>                             
var list = new List<int>();

Func<TSource, bool> 

var items = Enumerable.Range(1, 0).Select(d => new { пустое моё })

if(что-то там)
{
var expr =
from c in customers
where c.City == "London"
select new{c.id, c.Name};
}
else
{
var expr =
from c in customers
where c.City == "Moscow"
select new{c.id, c.Name};
}

var items = Enumerable.Range(1, 100).Select(d => new { id = 0, Name = "" });

if(что-то там)
{
items  =
from c in customers
where c.City == "London"
select new{id = c.id, name =c.Name};
}

            var sts = new List<Student>
                          {
                              new Student{Name = "Vasya", Fak="U", Mark=5},
                              new Student{Name = "Vasya", Fak="U", Mark=5},
                              new Student{Name = "Vasya", Fak="U", Mark=5},
                              new Student{Name = "Vasya", Fak="U", Mark=5},
                              new Student{Name = "Petya", Fak="U", Mark=2},
                              new Student{Name = "Kolya", Fak="U", Mark=4},
                              new Student{Name = "Sasha", Fak="E", Mark=5},
                              new Student{Name = "Masha", Fak="E", Mark=4},
                              new Student{Name = "Masha", Fak="E", Mark=4},
                              new Student{Name = "Sveta", Fak="E", Mark=3},
                              new Student{Name = "Luda", Fak="F", Mark=1},
                              new Student{Name = "Max", Fak="F", Mark=5},
                              new Student{Name = "Alex", Fak="F", Mark=2},
                              new Student{Name = "Motya", Fak="F", Mark=5},
                              new Student{Name = "Gosha", Fak="F", Mark=2},
                              new Student{Name = "Samoil", Fak="V", Mark=3},
                              new Student{Name = "Michael", Fak="V", Mark=4},
                              new Student{Name = "Michael", Fak="V", Mark=4},
                              new Student{Name = "Murad", Fak="V", Mark=5},
                              new Student{Name = "Moton", Fak="V", Mark=3},
                              new Student{Name = "Fox", Fak="V", Mark=4},
                              new Student{Name = "Rabbit", Fak="V", Mark=5},
                              new Student{Name = "Rabbit", Fak="V", Mark=5},
                              new Student{Name = "Poter", Fak="H", Mark=3},
                              new Student{Name = "Fred", Fak="H", Mark=4},
                              new Student{Name = "Lisa", Fak="Y", Mark=5},
                          };

            if(true)
            {
                var expr =
                from c in sts
                where c.FakCity == "V"
                select new{c.Name, c.Mark};
            }
            else
            {
                var expr =
                from c in sts
                where c.FakCity == "H"
                select new { c.Name, c.Mark };
            }

public class Student
{
public string Name;
public string Fak;
public int Mark;
}

А вот, например, ещё ситуация.
а вот если мне в ифе, например нужно к sts сджойнить ещё одну таблицу, и вернуть также 
 select new { c.Name, c.Mark };

var q = from c in sts select c;